The invention is aimed in particular, although not exclusively, among these structures, at those intended to equip cable stayed bridges, suspension bridges or the like. The reinforcements habitually encountered in such structures comprise a certain number of wires.
In known embodiments of the reinforcements of the kind in question, the various constituent wires are generally twisted around a central wire. This arrangement is used to produce a strand, also known as a twist, made from wires of small diameter. The mechanical properties of the strand obtained are better than those of a single-wire strand in which the cross section of the single wire is equivalent to that of said strand.
Twisting the peripheral wires around a central wire secures the wires of the strand or twist together and reduces the flexural inertia of the assembly. A reinforcement unit is thus obtained from very high-strength wires.
However, producing the twisted strand or twist entails a special twisting operation which is expensive. In addition, this operation gives rise to differential elongation between the central wire and the peripheral wires. The peripheral wires are therefore less highly stressed than the central wire, giving rise to an apparent elastic modulus for the strand which is lower than that of each constituent wire.
Furthermore, the fatigue behavior of a strand as defined hereinabove is not as good as that of the wire of which it is made because the differential elongation between the peripheral wires and the central wire gives rise to differential movements with radial pressure and therefore to friction between the wires which is not really favorable in terms of fatigue.
An additional drawback lies in the work hardening that results from the twisting, which creates a stiff steel with residual internal tensions making it less ductile and therefore susceptible to creep or to relaxation, according to the type of loading. In order to attempt to reduce this drawback, an operation that consists in exerting tension under a high temperature close to 400xc2x0 C. is performed. This operation leads to additional cost and may be tricky because it demands a great deal of precision on the temperature when the wires are galvanized wires. This is because the melting point of zinc is not to be exceeded while at the same time not reducing the temperature too far as this would render the operation ineffective.
Furthermore, in order to obtain good protection against corrosion, it is common practice for a plastic film to be extruded over the strand. Prior to this extrusion operation, a spacer device allows the spaces between the wires around the central wire to be filled with a flexible product such as grease or wax. This operation, because of the need to untwist the wires and then twist them again, leads to further work hardening by deformation of the peripheral wires, which reduces the ductility of the strand.
The object of the invention is to overcome the aforementioned drawbacks by providing a reinforcement the mechanical performance of which is equivalent and even equal to that of each of the wires of which it is made.
To this end, according to the invention, a reinforcement of the kind in question is essentially characterized in that the wires are roughly mutually parallel to form a bundle and in that it comprises a plastic sheath which envelops the bundle, providing it with cohesion.
By virtue of this arrangement, the cohesion of the reinforcement obtained is preserved while the mechanical properties of the reinforcement are equivalent or equal to those of a constituent wire.
In preferred embodiments of the reinforcement according to the invention, recourse is further had to one and/or another of the following provisions:
the solid wires are metal wires and the sheath is made of flexible plastic extruded onto the bundle;
the solid wires are wires made of composite and the sheath is made of flexible plastic extruded onto the bundle;
the bundle of wires comprises a central wire and peripheral wires, the peripheral wires being tangential to the central wire and separated from one another, delimiting grooves;
the sheath has a cylindrical exterior shape and has a lobed interior wall with recesses and projections, the peripheral wires being housed in the recesses and the projections extending into the grooves;
the sheath has an exterior wall which in cross section is of circular shape;
the sheath has an exterior wall which in cross section is of a lobed shape;
the sheath has an exterior wall which in cross section is of roughly polygonal shape;
the sheath and the wires delimit gaps which are filled with a lubricant chosen from wax and grease; and
the sheath and the wires delimit gaps which are filled with a bonding device.
Furthermore, another subject of the invention is a cable for a building work structure comprising at least two reinforcements as defined hereinabove.
A further subject of the invention is a method for packaging a reinforcement as defined hereinabove by parallel winding onto a drum, making one full twist over one turn.
Finally, a subject of the invention is a method for implementing, in a building work, a reinforcement as defined hereinabove, consisting in that in at least one portion of the reinforcement, the solid wires are bared and the bared wires are anchored to at least a constituent part of the building work so as to cause the reinforcement to work in tension.
Advantageously, the collection of solid wires of the reinforcement are wedged collectively into an anchoring jaw assembly.